StarIDFromImage

Pyramid Star ID from a camera image
Info on the camera used to take the test image
Star catalog with appropriate limits
Process a stored image
Identify stars
Display results

Pyramid Star ID from a camera image

The focal length scaling must be known to high precision to successfully identify stars from a real image. The steps are written out here to be instructive but also see the listed support functions.

This demo identifies stars in a image of the Pleiades cluster, including some of its brightest stars:

17702: Alcyone, brightest star in the  Pleiades, magnitude 2.86
17499: Electra, magnitude 3.7
17573: Maia, magnitude 3.86
17608: Merope, magnitude 4.17
17531: Taygeta, magnitude 4.29

See also: LoadStarImage, FitHist, CoarseCentroids, ProcessCatalog, ProcessStarImage, StarIDPyramid, DrawStarImageCentroids

%--------------------------------------------------------------------------
%   Copyright (c) 2008 Princeton Satellite Systems, Inc.
%   All rights reserved.
%   Since 2019.1
%--------------------------------------------------------------------------

disp('Demo of StarIDPyramid, real image --')

Demo of StarIDPyramid, real image --

Info on the camera used to take the test image

nPixels  = 1024;    % image width in pixels, square in this case
pixWidth = 15;      % pixel size in microns
fLength  = 43.169;  % focal length in mm

% calculation field of view and scaling
fOV      = 2*atan(0.5*nPixels*pixWidth*1e-3/fLength);
fScale   = fLength/(pixWidth*1e-3);
pixRes   = fOV/nPixels;

Star catalog with appropriate limits

jD       = Date2JD([2016 1 1]);
minInt   = 6; % minimum intensity
angRes   = 5*pixRes;  % minimum resolution between stars
starData = ProcessCatalog( minInt,fOV,angRes,jD);

Keeping 2469 brightest stars across FOVs

Process a stored image

[pixels,d.img] = LoadStarImage( 'Plejades.tif', []);
nROI = 5;  % size of region of interest in pixels

% find the sky background in the image for thresholding
[bNoise,R] = FitHist( pixels );

% compute the centroids
optCOM = CoarseCentroids;
optCOM.T    = bNoise + 3*R;
optCOM.nROI = nROI;
optCOM.b    = bNoise;
[r0, iC, dCOM] = CoarseCentroids( pixels, optCOM, true );

Blob combine operations: 1

Identify stars

options               = StarIDPyramid;
options.pixelMapScale = fScale;
options.angleTolerance = 1.5*pixRes;

% transform centroids to center of image
starMeas = struct;
starMeas.pixelLocation = r0-nPixels/2;

starID = StarIDPyramid( starMeas, starData, options );

Display results

Hipparcos IDs of the stars

hipID = starData.starCatalog.name4(starID(starID~=0));
starID(starID~=0) = hipID;
fprintf('Star IDs:    %s\n',num2str(hipID));

DrawStarImageCentroids( pixels, r0(:,1:16), starID );


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